Vehicular rack and pinion steering systems include an elongated flat gear or rack having teeth which mesh with mating teeth of a rotating pinion gear. The pinion gear is rotatably mounted on a steering shaft. As a steering angle is imparted to the steering shaft via rotation of a steering wheel, the pinion gear translates along the rack via engagement with the rack teeth. This in turn moves the rack in a corresponding steering direction. Tie rods, which are disposed at the distal ends of the rack, are connected to front road wheels of a vehicle via a corresponding steering arm. Therefore, rack and pinion steering systems effectively convert rotational motion with respect to a steering axis into linear motion with respect to the rack, while also providing a suitable level of gear reduction.
Steering functionality provided by typical rack and pinion steering systems may be electrically assisted in some designs. For instance, an electric steering motor may be controlled to impart a variable steering torque overlay via a drive mechanism to the rack itself, i.e., a rack electric power steering (EPS) system, or along the steering axis in a pinion EPS or a column EPS system. While EPS systems of all types generally perform well under most driving conditions, a transient phenomenon involving a sudden increase in required steering effort followed by an abrupt reduction in steering resistance may manifest itself under certain driving conditions. Such a condition, referred to herein as a stick-slip condition, can impact steering quality and overall drive feel.